Raindrop counter

ABSTRACT

A flashing light freezes raindrops with respect to time, the shadows are focused on a vidicon which detects the shadows and converts them to ideal video pulses. The number of scan lines intersecting the drops is determined by a series of line counters and the count is decoded into channels and printed.

Unite States tent Stockham et al. Feb. 8, 1972 [54] RAINDROP COUNTER[56] References Cited [72] Inventors: John D- Stockham, Highland, Ind.;UNITED STATES PATENTS Lawrence B. Townsend, Downers Grove; Ronald L.ohlhaber, Evanston; Thomas Gerhardt M. Scopeljte, Flossmoor, ll f1113,061,672 10/1962 Wyle 3,408,485 10/1968 Scott ..235/92 PC [73]Assignee: The United States of America as "Pmemed by the Secretary ofAir Primary ExaminerMaynard R. Wilbur Fm'ce Assistant Examiner-Robert F.Gnuse 22 i 23 1970 Attorney-Harry A. Herbert, Jr. and Julian L. Siege![21] Appl. N0.: 100,977 57 ABSTRACT v A flashing light freezes raindropswith respect to time, the [52] US. Cl. ..235/92 PC, 235/92 R, 235/92 V,shadows are f d on a vidicon which detects the shadows 235/92 356/207and converts them to ideal video pulses. The number of scan [51] h t.Cl. ..G06m 11/04 lines intersecting the drops is determined by a Seriesf he [58] meld of Search "235/92 3 5 6xb 2 counters and the count isdecoded into channels and printed.

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SUMMARY OF THE INVENTION The images of raindrops falling in a controlledvolume are formed on a sequential scan vidicon. The light source is anintermittently flashed Xenon tube located at the focus of an opticalsystem. The tube is operated to freeze drops with respect to time.Parallel light is emitted from the optical system and directed throughthe rain field to the collector lens of the receiver. The parallel lightis focused onto the face of a vidicon receiver by a telecentric opticalsystem having selectable magnifications. The volume of rain field viewedis defined by the distance between the two movable hoods and thecrosssectional area of the parallel light beam which is focused onto thevidicon. The telecentric optical system ensures that only parallel lightentering the receiver lens along the optic axis is transmitted to thevidicon. In this way stray light from external source is eliminated fromthe vidicons field of view.

The image on the vidicon of a raindrop in the field of view isinterrogated by the horizontal sequentially scanning beam of thevidicon. The number of scan lines intersecting the drop is determined,classified into a channel of specified line number ranges and related byprior calibration to the vertical height of the drop. In order toincrease the number of drops counted, provision is made for simultaneouscounting and sorting of a plurality of drops on each scan line. Assuminga log-normal rain distribution randomly distributed in space, arestriction of up to four drops corresponds to a drop density of up to20 particles per field of view. Thus under optimum conditions thecounter may detect the size up to 150 drops per second.

It is an object to provide a novel system for automatically counting andsizing raindrops.

It is another object to provide a raindrop counter that will operateequally well in sunlight or at night.

It is still another object to provide a raindrop counter that is capableof sizing drops between one-fourth and 4 millimeters.

These and other objects, advantages, features and objects of theinvention will become more apparent from the following description takenin connection with the illustrative embodiment in the accompanyingdrawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows schematically the equipmentused on the optical bench when utilizing the invention.

FIG. 2 is a block diagram of the electronic unit which contains themonitor to show the field of view being examined, the electronic signaldata handling logic, the instrument control logic, and the data printout.

FIG. 3 is a timing diagram used in vention.

FIG. 4 is a functional diagram of the decoder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The apparatus of FIG. 1can be mounted on an optical bench in an area in which the rainfall isto be measured. Flash lamp 11 at the focus of the optical system can bea Xenon tube and is activated and projected through aperture 13 usingmirror 15 and containing lens 17. The light iscollimated by collimatinglens 19 and passes through the rain field and through receiving lens 21and then through filter 23 and imaging lens 25. The beam then passesthrough lens turret 27 and light receiver 29. The lens turret permitsselectable magnifications. Adjustable hoods attached to lenses l9 and 21can be prothe explanation of the invided to slide along the opticalbench to limit the extent of the rain field falling between the lightsource 11 and light receiver 29.

Referring to FIG. 2, flash tube light source 31 provides theillumination to view the raindrops by vidicon 33. The duration of theflash is chosen to arrest the motion of the raindrops and the intensityof the flash is chosen to be operative in either night or sunlightconditions. To understand the functions performed by the electronicnetwork, assume that only one droplet image is on the vidicon 33, thatthe image is of such size that it is traversed by 10 scan lines, andthat these lines are numbered 300 to 309 in the video raster.

Reference to FIG. 3 showing the timing diagram aids the explanation. Thenumerical values shown representing pulse widths are in microseconds. Aflash of light is generated during vertical retrace prior to scan. Asscanning takes place, no signal is generated by lines numbered 1 to 299and 310 to 945, since they do not traverse a droplet image. Lines 300 to309 produce a pulse that is amplified by video amplifier 35 intelevision monitor 37. The droplet image is displayed by monitor display39 as a bright circle on a dark background. Each of the amplified pulsesgenerated by lines 300 to 309 is sequentially fed to video detector 41which analyzes the rising slope of the leading edge of the pulse withrespect to time.

A video pulse from line 300 on vidicon 33 is amplified and fed to videodetector 41. Video detector 41 identifies the pulse as a particle pulseand feeds a pulse to the ideal video generator 43 and generates an idealvideo pulse 4 psec. long and having 5 volt amplitude. This pulse issimultaneously fed to line counter l designated as 45 and to each ofthree delays, 47, 49 and 51. After delays of 250, 500 and 750 nsec.,respectively, the pulse is fed to line counters 2, 3 and 4 designated as47-49, respectively. The details of these subsequent line counters arethe same as that shown for line counter 1. Having been appropriatelydelayed and fed to one of the line counters, the pulse becomes aselected video pulse. The selected video pulse passes through input gate51 of line counter l and fires counter busy flip-flop 53 which in turnfires blanking pulse generator 55, the counter enable and the strobepulse generator 59. The blanking pulse generator produces a 5 psec.pulse that is fed to line counters 2, 3 and 4 within 250 nsec. of thebeginning of the ideal video pulse. Therefore the blanking pulse arrivesat line counters 2, 3 and 4 inputs before the delayed ideal video pulse.The selected video pulse is stopped at the input gates so counters 2, 3and 4 are not initiated.

Scan lines 311 through 900 continue with no counts recorded. Had aparticle been on lines 303 through 320, two ideal video pulses wouldhave been generated on scan lines 303 through 310. The second idealvideo pulse could not be handled by line counter 1 because it is onlycapable of measuring a particle at one position of the scan line. Thedelayed ideal video pulse passes through line counter 2 input gate. Thisselected video pulse fires the counter busy flip-flop which in turnfires the blanking pulse generator, the counter enable, and the strobepulse generator of line counter 2. The blanking pulse generator producesa 5 psec. pulse that is fed to line counters l, 3 and 4. The blankingpulse arrives at line counters 3 and 4 inputs before the delayed idealvideo pulse. The pulse that might have passed input gate 51 of linecounter 1 cannot pass because this counter will accept pulses only atone position in the horizontal scan. If a busy signal flip-flop 53 hasbeen fired in a particular line counter, the horizontal sync pulse fromcamera 33 is fed thru the counter enable to advance the line count byone.

The selected video pulse from scan line 300 also triggers the scandelay. The scan delay waits 34 psec. then triggers blanking pulsegenerator 55 and strobe pulse generator59 on line 304. This blankingpulse which blanks the other line counters occurs about 1 nsec. beforethe ideal video pulse should occur. The strobe pulse is compared withthe selected video as described above, and another horizontal sync pulseis counted in the counter of line counter 2.

On line 310, linecounter 1 transfers out as described above. Only oneideal video pulse occurs on each of scan lines 310 to 320, but linecounter 2 continues to count this particle, whereas line counter 1 doesnot see this particle. On scan line 321 the scan delay of line counter 2starts the blanking pulse generator and the strobe pulse generator justas it did in lines 304 through 320. The input gates of the other linecounters are blanked. The strobe pulse is compared with the selectedvideo in the pulse detector. Since there is no shadow intersection onthis line there is no ideal video pulse and hence no selected video. Thepulse detector triggers the transfer sequence just as line counter 1 didat the end of its particle. This time there were 18 counts stored in thecounter. The particle-size decoder decides this is a channel-4 particleso accumulator 4 is advanced one count. The above process can beperformed with up to four particles on one scan line in a similar manneras was described for two. FIG. 4 shows the functional relationship ofthe decoder. The decoder consists of a series of gates for selecting thecounts and is well known in the art.

At the end of the frame the ideal video generator and the TV monitor areinhibited for the next three scans. At the end of the fourth scan (thethird inhibited scan) the vertical retrace triggers flash lamp 31. Theideal video pulse generator and TV monitor display 39 are uninhibitedand the whole measuring procedure is repeated. This continues at therate of 7.5 samples per sec. for the sampling interval.

At the end of the sampling interval, the TV monitor display 39 and idealvideo generator 43 are inhibited, and the readout cycle is initiated. Aprint command is sent to printing recorder 75 to record sampling time inchannel 0. Part way through the print cycle the printer sends out a scanpulse that advances read out logic 77 one step, transfers the viewingvolume information to printer 75, and then sends out another printcommand to print the viewing volume in channel 1. Accumulators 73 areread out sequentially in a similar manner into channel 2 through 9 onthe printer. After channel 9 has been printed, a reset pulse is fed toaccumulators 73 and to the sampling timer 79. The instrument will beginto take data again as described above. Sampling is stopped by rotatingthe timer switch on the front panel to the manual position anddepressing the stop button. Read out logic 77 will print the time andall data stored before stopping.

We claim:

1. A system for analyzing a raindrop field comprising:

a. a flashing light source;

b. a vidicon camera with the rain field interposed between the lightsource and the vidicon camera;

c. a video detector fed by the camera;

d. an ideal video generator fed by the video detector;

e. a plurality of delays fed by the detector;

f. a first line counter and a plurality of delay line counters fedrespectively by the ideal video generator and the plurality of delays,each line counter including,

1. an input gate fed by the ideal video generator,

2. a counter busy flip-flop fed by the input gate,

3. a blanking pulse generator fed by the counter busy flipflop,

4. a counter enable circuit fed by the counter busy flipflop,

5. a strobe pulse generator fed by the counter busy flipflop,

6. a scan delay fed by the input gate and feeding the blanking pulsegenerator,

7. a pulse detector fed by the strobe pulse generator and the inputgate,

8. a transfer command circuit fed by the pulse generator,

9. an interval counter fed by the counter enable circuit and reset bythe transfer command circuit, and

10. a line count transfer gate fed by the interval counter and thetransfer command circuit;

g. a particle size decoder fed by the first line counter and having asequence of outputs; h. a sequence of accumulator channels fed by thesequence of outputs of the particle size decoder; and

i. a printer fed by the sequence of accumulator channels.

2. A system for analyzing a raindrop field according to claim 1 whichfurther comprises a timing control fed by the vidicon camera andtriggering the flashing light source and inhibiting the video generator.

3. A system for analyzing a raindrop field according to claim 2 whichfurther comprises a telecentric optical system interposed between theflashing light source and the vidicon camera, the optical system havinga turret controlled interchangeable magnifying lens.

1. A system for analyzing a raindrop field comprising: a. a flashinglight source; b. a vidicon camera with the rain field interposed betweenthe light source and the Vidicon camera; c. a video detector fed by thecamera; d. an ideal video generator fed by the video detector; e. aplurality of delays fed by the detector; f. a first line counter and aplurality of delay line counters fed respectively by the ideal videogenerator and the plurality of delays, each line counter including, 1.an input gate fed by the ideal video generator,
 2. a counter busyflip-flop fed by the input gate,
 3. a blanking pulse generator fed bythe counter busy flipflop,
 4. a counter enable circuit fed by thecounter busy flip-flop,
 5. a strobe pulse generator fed by the counterbusy flip-flop,
 6. a scan delay fed by the input gate and feeding theblanking pulse generator,
 7. a pulse detector fed by the strobe pulsegenerator and the input gate,
 8. a transfer command circuit fed by thepulse generator,
 9. an interval counter fed by the counter enablecircuit and reset by the transfer command circuit, and
 10. a line counttransfer gate fed by the interval counter and the transfer commandcircuit; g. a particle size decoder fed by the first line counter andhaving a sequence of outputs; h. a sequence of accumulator channels fedby the sequence of outputs of the particle size decoder; and i. aprinter fed by the sequence of accumulator channels.
 2. a counter busyflip-flop fed by the input gate,
 2. A system for analyzing a raindropfield according to claim 1 which further comprises a timing control fedby the vidicon camera and triggering the flashing light source andinhibiting the video generator.
 3. A system for analyzing a raindropfield according to claim 2 which further comprises a telecentric opticalsystem interposed between the flashing light source and the vidiconcamera, the optical system having a turret controlled interchangeablemagnifying lens.
 3. a blanking pulse generator fed by the counter busyflip-flop,
 4. a counter enable circuit fed by the counter busyflip-flop,
 5. a strobe pulse generator fed by the counter busyflip-flop,
 6. a scan delay fed by the input gate and feeding theblanking pulse generator,
 7. a pulse detector fed by the strobe pulsegenerator and the input gate,
 8. a transfer command circuit fed by thepulse generator,
 9. an interval counter fed by the counter enablecircuit and reset by the transfer command circuit, and
 10. a line counttransfer gate fed by the interval counter and the transfer commandcircuit; g. a particle size decoder fed by the first line counter andhaving a sequence of outputs; h. a sequence of accumulator channels fedby the sequence of outputs of the particle size decoder; and i. aprinter fed by the sequence of accumulator channels.